Halide perovskites are promising candidates for soft X-ray detection (<80 keV) owing to their high X-ray absorption coefficient, resistivity, and mobility lifetime product. However, the lack of large high-quality single crystals (SCs) renders it challenging to manufacture robust hard X-ray imaging systems (>100 keV) with a low detection limit and stable dark current. Herein, high-quality inch-size two-dimensional (2D) Cs 3 Bi 2 Br 9 (CBB) single crystals are grown from a melt via the Bridgman method. The crystal quality is enhanced by eliminating inclusions of CsBr-rich phases and restraining the trap-state density, leading to an enhanced resistivity of 1.41 × 10 12 Ω cm and a mobility lifetime product of 8.32 × 10 −4 cm 2 V −1 . The Au/CBB/Au singlecrystal device exhibits a high sensitivity of 1705 μC Gy air −1 cm −2 in all-inorganic bismuth-based perovskites and an ultralow detection limit of 0.58 nGy air s −1 in all of the bismuth-based perovskites for 120 keV hard X-ray detection. The CBB detector exhibits high work stability with an ultralow dark current drift of 2.8 × 10 −10 nA cm −1 s −1 V −1 and long-term air environment reliability under a high electric field of 10 000 V cm −1 owing to the ultrahigh ionic activation energy of the 2D structure. The proposed robust imaging system based on CBB SC is a promising tool for X-ray medical imaging and diagnostics. KEYWORDS: lead-free perovskites, two-dimensional perovskites, Cs 3 Bi 2 Br 9 single crystal, ultralow detection limit, X-ray imaging

In particular, various X-ray applications with different energies result in different requirements for the detector. For instance, both X-ray diffraction (XRD) and X-ray fluorescence mainly need to detect X-rays with energies lower than 10 keV in scientific research. In contrast, X-rays with energy of 25-50 keV are used to produce images in mammography and chest radiography, [4] while computed tomography (CT) is equipped with digital X-ray image detectors with energy of 80-150 keV. [5,6] Current semiconductor materials such as Si, α-Se, HgI 2 , PbI 2 , and CdZnTe (CZT) are widely applied in direct detectors but suffer from some drawbacks. [7][8][9] Si and α-Se detectors have small attenuation coefficients for light atoms that limit the detection of X-rays to less than 50 keV. HgI 2 and PbI 2 detectors have large leakage currents and poor stability. A commercial CZT detector, which has excellent energy resolution and good photopeak efficiency, is expensive for single crystal (SC) growth and suffers from defects related to charge trapping. [10] Therefore, it is necessary to explore new materials for high-performance radiation detection.In recent years, metal halide perovskites have attracted increasing attention for room-temperature nuclear radiation detection due to their high atomic number (Cs,55, Pb, 82, Br, 35 and I,53), tunable band gap (E g = 1.56-3 eV), [11,12] high resistivity (R = 10 7 -10 12 Ω cm), [13,14] large mobility lifetime product (μτ = 10 −5 to 10 −2 cm 2 V −1 ), [15,16] and low cost in SC growth. These advantageous properties result in large ray attenuation and increased carrier collection efficiency (CCE) for both perovskite SCs and polycrystalline thin films. However, despite their high sensitivity of ≈10 6 -10 8 µC Gy −1 cm −2 , which is two to seven orders of magnitude higher than that of α-Se (20 µC Gy −1 cm −2 ) and CZT (12 000 µC Gy −1 cm −2 ), [17,18] and extremely low detection limit of 0.61 nGy s −1 , which is four orders of magnitude smaller than regular medical diagnostic requirement of 5.5 εGy s −1 , [19] previous studies conducted using these materials have mainly focused on the detection of soft X-rays with energy of several to tens of keV. [18,[20][21][22][23] Few studies have been performed on detecting hard X-rays, specifically in the range greater than 100 keV, which is required in CT imaging and positron emission tomography. In fact, the penetration depthsThe relatively low resistivity and severe ion migration in CsPbBr 3 significantly degrade the performance of X-ray detectors due to their high detection limit and current drift. The electrical properties and X-ray detection performances of CsPbBr 3 −nIn single crystals are investigated by doping the iodine atoms into the melt-grown CsPbBr 3 . The resistivity of CsPbBr 3 −nIn single crystals increases from 3.6 × 10 9 (CsPbBr 3 ) to 2.2 × 10 11 (CsPbBr 2 I) Ω cm, restraining the leak current and decreasing the detection limit of the detector. Additionally, CsPbBr 3 −nIn single crystals exhibit stable dark currents, arising fro...

The long-wave infrared acousto-optic tunable filters (AOTFs) based on Hg2Br2 crystals have attracted much interest in space exploration and harmful chemical agent detection. However, the growth of large Hg2Br2 single crystals with high quality and optical homogeneity still remains a challenge, and the lack of temperature-dependent mechanical and thermal properties of this crystal hinders the further enhancement of acousto-optic performance in practical applications. In this context, Hg2Br2 crystals (Φ 35 × 40 mm3) were successfully grown by the physical vapor transport (PVT) method. The optical homogeneity of the as-grown crystal is increased to 7.15 × 10–5 by restraining the impurities, striations, and cracks. In addition, the anisotropic mechanical and thermal properties varying with the temperature of Hg2Br2 crystals were systematically investigated. The compression modulus along the ⟨110⟩ orientation decreases from 17 to 7 GPa in the temperature range of −100 to 150 °C, while it ranges from 5.5 to 1.5 GPa along the ⟨001⟩ orientation. The thermal conductivities along ⟨110⟩ and ⟨001⟩ orientations vary in the range of 1.32–0.52 and 2.06–1.05 W/(m·K) with the increase in temperature from −140 to 100 °C, respectively, and then remain stable in the range of 100–150 °C. Using the first-principles calculation on the electron transfer characteristic between atoms and the bonding property within molecules of Hg2Br2 crystals, the large anisotropic mechanical and thermal properties could be explained, which are mainly attributed to the one-dimensional chain structure of the compound. Notably, the mechanical and thermal properties of Hg2Br2 crystals at low temperature are better than those at high temperature, which guarantees the practical application of AOTFs in a space extreme environment.

Mercurous halide crystals which crystallize in one-dimensional chain-like structure have attracted great attention as polarized and acousto-optic devices in long wave infrared range for their large birefringence, wide transparent range,...

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